In recent years, inorganic materials have come under review for their higher stability compared with organic materials. Ceramics led by alumina (Al2O3) and including steatite, zircon, cordierite and the like have found utility in many fields as functional materials making good use of properties specific to them, and their applications in electronic parts and components, semiconductor fabrication systems, and the like are increasing. For example, alumina is used as a functional material excellent in mechanical strength, electrical insulating properties, high frequency loss, etc. The assignee of this application has already found that among such alumina-based ceramics, a ceramic which is obtain able by conducting firing at from 1,400 to 1,700° C. in an air atmosphere and has a high alumina content of 95 mass % is excellent in thermal conductivity and thermal emissivity, and has already made a proposal about its use for cooling heat generating portion or portions (see Patent Document 1). As the ceramic is a noncombustible product having excellent electrical insulating properties and made of an inorganic material, cooling is feasible in direct contact with the heat generating portion or portions so that its use is expected in fields where cooling effects are desired including electronic devices, equipment and appliances.
Concerning alumina-based sintered bodies (ceramics) as functional materials, various other useful proposals have also been made for diverse applications with attention being focused on their mechanical properties, electrical properties and/or the like (see Patent Documents 2 to 7, etc.)
As those attracting attention in recent years from the viewpoint of environmental protection on a global scale, there are solar power generation devices employing power generation cells that make use of sunlight and luminescent devices with LED devices mounted thereon. From the viewpoints of making improvements in the conversion efficiency of energy or its luminous efficiency and achieving an extension in the service lives of products, it is desired for these devices to effectively cool the heat to be produced upon power generation or light emission (Patent Documents 8 to 10). The above-mentioned technology proposed by the assignee of this application and described in Patent Document 1 will be very useful if it can be applied.